1. Field of the Invention
The present invention concerns a method and a device for communication on an on-board network, in particular for a motor vehicle, compatible with the LIN standard, in order to optimise the load on this network.
2. Description of the Related Art
The use of an ever greater number of electromechanical devices in motor vehicles has led to an increase in the number of electrical circuits. In order to reduce the growing complexity of the wiring, “network” or “bus” techniques, already known in the computing field, have been adapted to the constraints of the automotive world.
The essential functions of vehicles are generally carried out “under the bonnet” by making use of a high-speed real-time network connecting the actuators and sensors of the engine, transmission, braking system, suspension, chassis, etc. to an electronic control unit (ECU). A Controller Area Network (CAN), providing a high degree of security and a transmission speed of the order of 1 Mbps, is frequently used for these functions.
For other less essential security functions and comfort functions, referred to as “passenger compartment functions”, a Local Interconnect Network (LIN) has been developed by motor vehicle constructors and semiconductor manufacturers.
This reduced-cost secondary network is based on a UART/SCI interface that is standard for the majority of microcontrollers. It works with the CAN bus and is used specifically for applications such as electric mirrors, electric seats, central locking, window regulators and lighting systems.
From the initial version 1.0 of 1999 up to version 2.0 of 2003, the specifications of the LIN network have gone through several developments tending to facilitate the integration of a network and improve the real-time characteristics.
All the details of these specifications are well known to persons skilled in the art, and only those necessary for understanding the invention will be repeated hereinafter.
Exchange of information on the LIN network is based on the presence of a master station and one or more slave stations. Communication is always carried out at the initiative of the master station which sends a message header comprising a silence followed by a synchronisation byte, and an identification byte or identifier.
A slave station having decoded a predetermined identifier transmits a data frame in response comprising two, four or eight data bytes and a checksum.
The header and data frame form a message frame.
It should be noted that the message identifier is representative of the content of the message, but not of its destination.
An identifier IDF[7:0] is formed from an identity ID[0:5] coded in six bits and two parity bits P0=ID0+ID1+ID2+ID4 (mod. 2) and P1=ID1+ID3+ID4+ID5 (mod. 2).
There are 64 different identities, but only the first 60 (00 to 3B, in hexadecimal representation) correspond to message frames.
The last four identities are special identities, in particular command frame, configuration and diagnostics identities.
The following table draws up a list of the valid identities and identifiers according to revision 2.0 of the LIN protocol specifications:
TABLE IIdentityIdentifierID[0:5]IDF[7:0]Frame type00 to 3BP1P0ID[5:0]Message frame3C3CCommand frame(request from the master station)3D7DCommand frame(response from the slavestation in the frame)3EFEUser-defined extended frame3FBFFuture extended frame
During the developments of the standard, the main characteristics of the LIN network were not fundamentally modified, and its transmission speed is still limited to 20 Kbps owing to constraints of electromagnetic compatibility and clock synchronisation without the use of a quartz crystal or ceramic resonator.
However, the “passenger compartment functions” prove to be increasingly greedy in terms of passband, in particular those relating to the AFS (Advanced/Adaptative Front Light System) advanced lighting system.
Directional lighting devices of the DBL (Dynamic Bending Light) type, or devices for automatic adjustment of the level of the headlight beams according to the attitude of the vehicle of the LVL (Levelling of Vehicle Light) category, connected by the network to the LCS (Light Control System) dedicated on-board computer, require very short response times.
Extension of the network to the control of future applications such as multi-xenon headlights, ballasts and LEDs will further increase the load on the bus.
A first solution for absorbing the increase in load on the network would be to increase the transmission speed thereof. But the initial advantages (low cost, low interference) of the LIN network would be lost.
A second solution would be to change standard and use more advanced networks such as CAN, but there again the cost would be prejudicial.
There is therefore a need for optimising the load on a LIN network in order to retain this economical standard for all the “passenger compartment functions”, and especially the management of AFS type advanced lighting systems, both present and future.